Gaseous conduction lamp



Aug. 26, 1930.

F. SKAUPY ET AL GASEOUS CONDUCTION LAMP Filed Jan. 24, 1927 Inventor-s Franz SKaupy.

Hans Ewest.

Hans PulFrich.

Walterschallreut ter; by may "Fl-weir- Amber-neg.

Patented Aug. 26, 1930 UNITED STATES PATENT OFFICE FRANZ SKAUPY, OF LICHTERFELDE, BERLIN, HANS EWEST, OF BERLIN, HANS PUL- FBICH, 0F BAUMSCHULENWEG, BERLIN, AND WALTER SCHALLREUTTEB, OF SGHONEBERG, BERLIN, GERMANY, ASSIGNORS 130 GENERAL ELECTRIC COMPANY, A

CORPORATION OF NEW YORK GASEOUB CONDUG'IION LAMP Appllcatl on filed. January 24, 1827, SerialNo. 163,089, and in Germany January 28, 1928.

Gaseous conduction electric lamps filled with nitrogen usually have a very low gas pressure, about that of a mercury column,

7 of 1 mm. or even less, and the pressure of the as the .gas pressure decreases, are to automatically supply some nitrogen as a result of being heated y the action of the electrical discharge. This plan has never attained practical importance, because the discharge passes over to the auxiliary electrodes only in response to a considerable decrease in pressure and the considerable increase in load current produced thereby, and therefore only when the tube already shows, due to the considerable decrease in pressure, a disagreeable discoloration of its normally yellow luminous positive column. If the nitrogen is to be supplied before the pressure decreases to that extent, a special heatin of the auxiliary electrodes is necessary, w ch, however, complicates the device.

These drawbacks to the practical use of substances which evolve nitrogen when heated are such that so far no attempts have been made to use such gas supplying substances in tubes without auxiliary electrodes by placing the substances directly on or in the main electrodes. The reason may lie in the assumption that the heating would be so great as to cause dangerous overfeeding of the tube, since the gas-supplying substance would continually be exposed to heating due to the current through the lamp.

It has however been found very unexpectedly that with proper dimensions and arrangement of main electrodes constantly connected in the discharge path, there be constantly obtained from substances, such'as alkali or earth alkali metal asides put into or attached to the main electrodes approximately as much gas, particularly nitrogen, as is consumed by the discharge. It is necessary that the size of the electrodes be such that in their normal operation the action of the adherent glow does not heat them up to the normal decomposing point of the substance (with sodium azide for example 330 C.) but does constantly maintain them at least at such a temperature (with sodium azide for example 200 to 300 C.) that there occurs in the tube a slight, but suificient evolution of nitrogen. If the electrodes are too large then the temperature required for the slow evolution of gas is not obtained during normal operation, and not even when the load current increases, because then the only result 1s further spreading of the glow along the electrode but without a noticeable increase of its temperature. Electrodes which are too small become too hot from the beginning causing a steady and excessive evolution oi gas by which the tube isvery soon overfed.

In accordance with the invention the electrodes are so formed that if the steady slow feed of gas is not sufiicient, then there occurs a temporary increase in the intensity of the glow and as a result an increased supply of gas. With the evolution of the gas and resulting increase in pressure the load current at once correspondingly decreases and with it the density of the glow and also the heating of the electrode so that again a safe and slow feed of gas is produced. The gas feed isthereby rendered extremely sensitive and its regulation is entirely automatic.

A specially great sensitiveness and a. reliable operation of the gas feed is obtained if the glow is forced to form on the interior surface of a hollow cylindrical electrode fitting with slight clearance in the enclosing glass vessel with its open end toward the path of discharge, and having at the other enda container preferably cone-shaped to contain the azide or similar nitrogen evolviLg compound. In this case, the azide container lying at the bottom of the electrode is subjected to especially high temperature variations with the slightest changes in the gas pressure and the load current.

One example of construction of lamp made in accordance with the invention is shown in the accompanying drawing, which is a longitudinal section of an electrode and the end chamber of the lamp.

The lamp tube a is enlarged in the usual manner at each end to form a chamber 1), into which a tubular cup shaped electrode is set. The leading in wire (1 for the electrode is sealed airtight into the stem 6 of the chamber. The electrode is a hollow cylinder of a suitable metal such as iron and is open toward the path of the discharge through the tube a. The electrode is mounted in the chamber 6 with but slight clearance. At the other end of the electrode a there is a transverse portion in the form of a cone-shaped container f which forms at the same time the bottom of the cup shaped electrode. This container is closed by a loose cover g, for example, fastened in lace by means ofa bayonet lock and connected with the leading in wire (Z. The cone-shaped container f with the apex turned toward the path of the discharge is filled with a powder-like azide, for example, sodium azide placed loosely in the container and kept in place by a plug or packing of glass wool 5.

Assuming that the discharge tube a has with an inner diameter of m. 111. a length of about one meter or more, and that the pressure of the nitrogen filling is that of a mercury column of 1 mm., then with a normal load current of about 150 milliamperes the size of the electrode 0 must be such that the interior surface of the cylindrical electrode, inclusive of the surface of the container 7", turned toward the discharge path, amounts to about 280 square centimeters. The glow formed when the current flows then develops, as indicated in narrow dotted lines in, very plainly along the forward edge or rim of the cylindrical electrode 0, and gradually de-' creases in intensity toward the interior of the electrode until near the bottom of the electrode it is in a barely perceivable thin fluffy state. Only at the projecting point of the container 7 does there develop, because of the action of the point, a somewhat more plainly discernible glow. On the outside of the electrode 0 the glow cannot develop because of the slight clearance around the electrode. By the action of the glow thus definitely regulated in its formation the electrode is normally heated only up to about 200 to 800 C. thus being kept at a temperature below 330 0., the temperature of decomposition of the sodium azide at atmospheric pressure. This heating suflices or almost suffices to secure a steady slow feed of nitrogen for there occurs spontaneously in a vacuum a perceptible "decomposition of the sodium azide at slightly above 190 C. Through the fine slot m between the loose cover 9 and the rear edge of the container f, or else through a fine hole at the oint o the container f, the nitrogen, stea ily developed in small quantities, passes over into the tube a and replenishes its nitrogen content so that the normal nitrogen pressure is permanently mamtained.

Should the gas replenishment for any reason, for example with too low an outside temperature, be exceptionally insuflicient and the pressure in the tube drop to about 0.9 mm. or below, then the load current of the tube will, because of the drop in pressure, increase automatically in the usual manner to about 17 0 to 200 milliamperes. The glow then increases considerably in consequence of the dimensions of the electrode, so that, as indicated in striated lines I, not only the entire interior surface of the cylindrical electrode, but also the outer surface of the cone-shaped container is covered with a luminous glow. As the increase in the glow develops gradually the impression is given, that the glow creeps into the interior of the electrode when the load current increases. As soon, however, as the glow increases in this manner, the electrode c and with it the container f will be more highly heated, that is to 330 (1, and over. lVith such a heating the normal decomposition temperature of the azide is exceeded, and there thus takes place momentarily a strong evolution of nitrogen, which immediately stops of itself when the normal nitrogen pressure in the tube is reached in consequence of the decrease in load current and the return of the glow to the position shown in dotted line is, so that an over-feeding of the tube with nitrogen cannot occur. lVhat we claim as new and desire to secure by Letters Patent of the United States, is:

l. A gaseous conduction lamp comprising a discharge tube containing nitrogen, a pair of nain electrodes in said tube, one of which is cup shaped and fits into the end of said tube with slight clearance with its open end toward the path of thedischarge, a cone-shaped container within and at the bottom of said electrode, and a nitrogen evolving compound in said container.

2. A gaseous conduction lamp comprising a discharge tube containing a gas at low pressure, a pair of main electrodes in said tube, one of which is cup-shaped and fits into the end of said tube with such slight clearance that no discharge occurs in the space between said electrode and said tube and with its open end toward the path of the discharge, a cone shaped container with perforated walls mounted within and at the bottom of said electrode with its apex toward the open end of said electrode, and a compound in said container which slowly evolves gas at the temperature attained by the walls of said container during normal operation of the tube.

3. A gaseous conduction lamp comprising a discharge tube containing a-gas at low pressure, a pair of main electrodes in said tube one of which is cup-shaped and fits into the end of said tube with such slight clearance that no discharge occurs in the space between said electrode and said tube, and with its open end toward the path of the discharge, a conical container perforated near the apex and having an altitude less than the depth of said cup and its base at the bottom of said cup whereby under normal conditions the major portion of the glow discharge on the electrode occurs at the edge of said cup and the minor portion on said container, and a 1 compound in said container which in response'to the discharge under normal conditions slowly evolves the same gas as that originally present in the tube.

4:- A gaseous conduction lamp comprising a discharge tube containing a gas at low pressure, a pair of main electrodes in said tube, one of which is cup-shaped and fits into the endof said tube with such slight clearance that no discharge occurs in the space between said electrode and said tube and with its open end toward the path of discharge, a conical metal container having an altitude less than the depth of said cup and with walls perforated throughout their extent and its base at the bottom of said cup whereby under normal conditions the major portion of the glow discharge on the electrode occurs at the edge of said cup and the minor portion on the perforated walls of said container, and a powdered compound loose in said container and in contact with said perforated walls which slowly evolves in response to discharge under normal conditions, the same gas as that originally present in the tube.

5. A gaseous conduction device comprising a discharge tube containing a conducting gas, a pair of electrodes in said tube, one of which is annular and fits into said tube with such slight clearance as to prevent discharge in the space between said electrode and the walls of said tube, and has a portion extending transversely of its bore behind the forward edge of said annular electrode to be further from the main. discharge than the forward edge of said electrode and to be exposed through the bore of said annular electrode to the discharge in said tube, and a material in thermal relation to said transverse portion such that in normal operation the discharge to said portion causes slow evolution of said gas.

6. A gaseous conduction device comprising a discharge tube containing a conducting gas, a pair of electrodes in said tube one of which is tubular and fits into said tube with such slight clearance as to prevent discharge in the space between said electrode and the ture of normal operation evolves said gas.

very slowly.

In witness whereof, we have hereunto set our hands this 10th day of January 1926.

FRANZ SKAUPY. HANS EWEST. HANS PULFRICH. WALTER SCHALLREUTTER. 

